Lasers utilizing an alkali vapor are relatively new. In these lasers, the alkali atoms are excited from the ground 2S1/2 state to the excited 2P3/2 state by absorption of laser diode pump light and lased from the 2P1/2 state that lies just below the pumped level. Non-radiative interstate relaxation between the 2P3/2 and the 2P1/2 state may be achieved through collisional deexcitation or energy transfer to a molecule, for example ethane. Because the lasing energy photon is just slightly less than the exciting photon, these lasers may be very efficient. Also, the fact that these lasers use a low density vapor means that there may be little wave front distortion.
Alkali lasers have been made using potassium, rubidium, and cesium vapors. As shown in FIG. 1, which shows the energy levels involved in lasing a rubidium line in an alkali laser, the pump photon energy (780 nm) is just slightly higher than the lasing photon energy (795 nm). The use of a vapor requires either that the vapor be of a fairly high concentration or that a reasonably long path length be provided to absorb all of the pump radiation. However, because these alkalis are very reactive materials which are commonly used for reflective and antireflective surfaces within lasers are susceptible to alkali attack, and therefore are generally poor choices for use in alkali lasers and other devices which use alkali gas.
Therefore, it would be very beneficial to have an alkali resistant material and/or coating capable of being used in alkali lasers and other devices which use alkali gas that will not be chemically attacked or allow the alkali to diffuse, but also is highly reflective or lowly reflective.